Cracking catalysts are solid particles which catalyze the cracking of long chain hydrocarbons found in crude oil into shorter chain and more valuable hydrocarbons.
As a result of this process, spent catalyst particles are produced. These particles contain adsorbed hydrocarbons. For maximizing yield from the cracking process and to reutilize the catalyst, it is necessary to strip the adsorbed hydrocarbons from the particles. Such a stripping process typically occurs in a pressurized stripping vessel. Pressurization is needed since the stripping vessel is part of the overall process loop which includes the catalytic riser reactor and catalyst regenerator. To minimize power consumption, it is essential not to release pressure which occurs in the refinery process. Since pressurized vessels are costly, it is desirable not to size the vessels larger than necessary.
In the stripping vessel, a stripping gas such as steam is typically passed through a fluidized bed of catalyst particles. The steam is at an elevated temperature and strips at least some of the adsorbed hydrocarbons from the particles. The velocity of the steam, however, is sufficient to entrain some of the catalyst particles as the steam passes through the bed. After stripping the adsorbed hydrocarbons from the particles it is desired to pass those hydrocarbons on for further processing or collect them as end products. In either case, it is undesirable to have entrained catalyst particles in this stripped hydrocarbon product. Hence, it is necessary to separate these entrained particles from the stripped hydrocarbons.
Cyclones are a typical piece of apparatus used for solid-gas separation. Some cyclones have quite high separation efficiencies. By their nature, however, they are large and cumbersome in size and construction. A cyclone could be placed in the upper portion of the stripping vessel, but this would necessitate enlarging the vessel beyond the size necessary merely for the stripping process. The cyclone could be placed outside the vessel, but then another pressure vessel would be needed to contain the cyclone. Each alternative presents increased cost and maintenance concerns.
Technologies other than oil refining also require separation of solids and gases. Such processes include polymerization processes. Some polymerization processes result in a vessel containing the solid polymer product and some unreacted monomer feed components. To maximize yield and improve consistency of the polymer product, it is desired to separate the unreacted monomer from the polymer product. Such separation can be achieved in a stripping process similar to that used in the catalytic particle process discussed in the preceding paragraphs.
That is, a stripping gas such as steam is passed upward through a bed of the monomer/polymer mixture. The steam is at elevated temperatures and strips at least some of the monomer from the polymer. However, some of the polymer becomes entrained in the steam as it passes upward through the bed. Other solid-gas separation exist and include removing particulates from a factory environment. Typical removal technology currently in use involve large ventilation fans. Such fans have disadvantages of excessive noise, capital expense, and high power consumption.
Accordingly, It would be desirable to find a separation apparatus and process that did not require substantial head room in the stripping vessel or other type vessel and did not require a separate pressure vessel.